Process for continuous casting of metal billets



May 29, 1956 s. JUNGHANS 2,747,245

PROCESS FOR CONTINUOUS CASTING OF METAL BILLETS Filed June 29, 1951 J Ey i 6 m 7 k 5 710a INVENTOR S/EGFR/ED JUNGHANS ATTORNEYS United StatesPatent 7 PROCESS FOR CONTINUOUS CASTING OF METAL BILLETS SiegfriedJunghans, Schorndorf, Germany Application June 29, 1951, Serial No.234,195

2 Claims. (Cl. 22200.1)

The present invention relates to a process for the continuous casting ofmetal billets and in particular billets of metals having a high meltingpoint such as iron and steel.

It is an object of the invention to provide a process which renders itpossible to produce a billet by continuous casting, which billet isparticularly dense and free of pipes or axial cavities, segregations andinternal cracks.

It has been found in accordance with the invention that the desiredimprovement in the properties of the continuous cast billet can beefiected primarily by the applications of pressure upon the moltencharge as it solidifies. It was found, furthermore, that continuouscasting particularly olfers the possibility of applying an elfectivepressure, especially when the following procedure, in accordance Withthe invention, is employed: The molten metal at the edge zone of thecross-section of the casting is solidified a short distance from theupper surface into a closed, substantially rigid, conveyable casing orcrust as it passes through a downwardly open cooled mold, whereascomplete solidification of the molten metal in the interior of thecasting is only eifected at such a distance from the upper surface ofthe molten metal that the existing pressure of the liquid headeflectively reduces the possibility of pipes or segregations. Incontinuous casting, the conditions of casting and cooling must beaccurately controlled in comparison to ordinary casting of ingots. Ithas been found from experience that the continuously cast billet,because of this accurate control, solidified homogeneously with ratherirregular orientation of the crystals formed, particularly, at itscenter. The process, in accordance with the invention, can, therefore,be carried out with columns of molten metal of a height which could notever be remotely approached in ordinary ingot casting processes becauseof the danger of interruptions in the fluid column because of bridgingas a consequence of dendritic crystal growth.

It was found desirable to carry out the cooling of the solidified casingand its inner fluid core in such a manner that the greatest possiblecross-section is subjected to the fluid pressure. Consequently, it wasfound desirable only to remove so much heat from the billet while itpasses through the mold, that the equilibrium temperature reachedbetween the solidified casing and the inner molten portion after itleaves such mold is just below the melting point. An additionalcharacteristic of the invention resides in the regulation of the shapeand depth of the molten inner portion of the billet ice cracks. It wasunexpectedly found, in accordance withthe invention, that such internalcracks were caused by the mechanical means employed for controlling thebillet; speed through the mold. These means, in continuously operatingcontinuous casting plants, normally consistsof clamping rollers whichserve to reduce the speed at which the heavy billet descends to theselected rate of casting. Previously, it had not been recognized thatproper application of such means is of great importancein the productionof sound castings. In accordance with the invention, it was found thatthe clamping pressure of the means employed can lead to inner axialcracks; because of the squeezing action effected thereby on theinsufficiently solidified billet. Consequently, an additionalcharacteristic of the invention is that clamping pressures of the meansfor controlling the speed of the billet through the mold are onlyapplied at a point where the billet has solidified sufficiently to beable to resist the pressure stresses which might cause damage to itsstructure. This point normally lies below the tip of the column ofmolten metal. As the billet with its very deep column of molten metalnormally does not have sufficient inherent stiflness to prevent itsbending out of its direction of travel before it reaches the clampingrollers or other means employed to control its descent, it can bedesirable to provide lateral guiding means for the billet which exertsubstantially no pressure thereupon.

The casting apparatus for carrying out this modification of theinvention should be provided with means for controlling the billet speedthrough the mold whose distance from the lower end of the mold can beadjusted and, furthermore, with guiding means such as, for example,rollers or similar devices that can be contacted with the billet inaccordance with the requirements of the individual instance to preventsagging or bending of the billet on its way from the mold to the meanscontrolling the descent of the billet.

Further objects and advantages of the invention will become apparentfrom the following description taken together with the drawings.

In the drawings:

Fig. I schematically shows a vertical section of an apparatus suitablefor carrying out the process in accordance with the invention.

Fig. 11 shows a cross-section through a faulty billet.

In Fig. I, runner 1 which is supplied with molten metal from a suitablesource, delivers molten metal to the top of the water-cooled,downwardly-open mold 2, wherein the fluid metal is so sharply cooledthat a solidified casing S1 is quickly formed around the still fluidcore S2 of the billet S being cast, which casing extends substantiallyup to the upper surface S3 of the molten metal.

After the embryo billet leaves the lower end of mold 2, its solidifiedcasing S1 must be maintained at a predetermined thickness and it as wellas the liquid core S2, must be maintained at predetermined temperatures.For this purpose, the billet is passed through an equalizing chamber 3,which, for example, can be filled with hot air, steam or a hot gas suchas nitrogen or other neutral gas. Chamber 3 is merely shownschematically. Appropriate means can be provided therein to effect thecooling at a predetermined rate. For example, the chamber can besubdivided into several zones provided with different cooling media or acooling medium at different temperatures. The gas chamber 3 must be ofsuflicient length that a fluid column S2 is maintained which issufliciently high that its fluid pressure effectively reduces oreliminates the formation of pipes and/or segregations within the billet.

The complete solidification of the billet S occurs at:

metal. In the case of a steel billet having a diameter of 100 mm. and itwas found that a column of molten metal of a length L of 2400 mm.provided a fluid pressure head of 1.7 atmospheres gauge pressure. Thebillet leaves mold 2 with a surface temperature of about 1350 C., and isthen passed through a gas chamber, the temperature of which is adjustedto about 600 C. After passing through the gas chamber, the billet has asurface temperature of about 1150 C. The resulting billet was of soundstructure in which no spongy spots or segregations could be discovered.

Rollers and 6, whose speed of rotation is controlled by shaft 7, areprovided to control the descent of billet S. The rollers 5 and 6, whenthere is danger of internal cracking, should grip the billet below thelower tip S4 of the liquid core S2.

It is easily ascertainable whether interior cracks in the billet arecaused by premature application of the clamping of rollers 5 and 6 byinterrupting the casting and permitting a portion of the billet abovethe rollers to solidify completely. A cross-section of the billet willshow an axial inner crack S5 (Fig. II) which extends between points Q1and Q2 of the clamping pressure if the clamping pressure has beenapplied prematurely. Consequently, if such a crack is formed, therollers must be adjusted to a lower position.

As the billet leaves mold 2 with a surface temperature of about 1250" to1350 C. and with a liquid core and will remain so for several moldlengths, nonpropelled guide rollers 8a and 8b and 9a and 9b are providedto prevent possible lateral bending or breaking of the billet aboverollers 5 and 6. A spraying device 10 is positioned below the mold 2 forthe purpose to maintain the solidified casing S1 at a predeterminedthickness, i. e. to prevent that the liquid core S2 is melting andfinally breaking through the casing S1, until the billet S has enteredthe gas chamber 3.

Spraying device 10 can be omitted if the billet is cooled by means ofthe mold 2 to such an extent, that with the gas chamber 3 positionedclosely to the mold, there is no danger that the liquid core could breakthrough between the different cooling steps of the billet.

I claim:

1. A process for the continuous casting of metal billets comprisingcontinuously pouring molten metal into an open mold shell, cooling themolten metal and thereby forming an embryo billet composed of asolidified casing about a molten core, withdrawing the embryo billetfrom the bottom of the mold, then reducing the cooling by hot gas meansin order to maintain the molten core at a depth suflicient for its fluidpressure to eliminate segregations, while at the same time laterallysupporting the billet without distortion pressure thereon, solidifyingsaid billet adjacent the bottom of said gas means, and then grippingsaid billet with billet withdrawal means adjacent the lower end of themolten core at a point where the billet has obtained sufiicientsolidification to Withstand the pressure of the gripping means withoutforming fissures in the solidified billet.

2. A process as in claim 1, further comprising water cooling said billetbetween the mold and the gas means to further preserve said solidifiedcasing.

References Cited in the file of this patent UNITED STATES PATENTS648,091 Trotz Apr. 24, 1900 894,410 Trotz July 28, 1908 2,195,809Betterton et al Apr. 2, 1940 2,284,503 Williams May 26, 1942 2,284,703Welblund et al June 2, 1942 2,284,704 Welblund et al June 2, 19422,590,311 Harter et a1 Mar. 25, 1952

1. A PROCESS FOR THE CONTINUOUS CASTING OF METAL BILLETS COMPRISINGCONTINUOUSLY PORING MOLTEN METAL INTO AN OPEN MOLD SHELL, COOLING THEMOLTEN METAL AND THEREBY FORMING AN EMBRYO BILLET COMPOSED OF ASOLIDIFIED CASING ABOUT A MOLTEN CORE, WITHDRAWING THE EMBRYO BILLETFROM THE BOTTOM OF THE MOLD, THEN REDUCING THE COOLING BY HOT GAS MEANSIN ORDER TO MAINTAIN THE MOLTEN CORE AT A DEPTH SUFFICIENT FOR ITS FLUIDPRESSURE TO ELIMINATE